Fuze



Aug- 11 1959 L. R. HAFsTAD ErAL 2,898,857

FUZE

Filed Aug.-7, 1944 5 Sheets-Sheet 1 AFSTAD A ORNEY A118- lll, 1959 L. R.HAFs-rD Erm. 2,898,857

FUZE

5 Sheets-Sheet 2l Filed Aug. 7, 1944 LAwREA/cyEA/fsma BY RICHARD ROBERTSATT EY lulg. 11, 1959 ,-R, HAFsxTAD ETAL 2,898,857

Filed Aug. 7, 1944 5 Shets-Sheet 5 W uvmkvb v INVN LAWRENCE TORS R.HFSTAD Bv RICHARD B. ROBERTS ATT L. R. HAFSTAD ETF AL Aug. 11, 1959 FUZE5 Sheets-Sheet 4 Filed Aug. 7, 1944 o mwv Mm mum Y wRMrMm ME n C D MM MHc, um

FIG. I4.

Aug. 11, 1959 l.. R. HAFs-TAD ErAL Fuzz:

Filed Aug'. 7, 1944 5 sheets-sheet s United Staes arent Y FUZE LawrenceR. Hafstad and Richard B. Roberts, Washington, D C., assignors to theUnitedStates of America as represented by the Secretary of the Navy Thisinvention relates lto photoelectric devices and has particular referenceto a novel light-sensitive fuze for explosive projectiles.

In the use of Va projectile against a target, such as an airplane, it isdesired to cause the projectile to explode at the target or in theimmediate vicinity thereof in order to produce maximum damage'.

An object of the present invention, therefore, is to provide a fuzewhich may be readily attached to projectiles of various types andV whichwill cause the projectile charge to explode when the projectile iswithin damaging range of an airplane, or other target, and at the properposition so that the fragmentation cone will intercept the target.

Another object is to provide'a fuze having a light-sensitive element[connected in an electrical circuit so that a changein the quantity oflight striking the element, due to the fuze approaching the target, willre a detonator, thereby causing the projectile to explode.

A further object of the invention resides in the provision of alight-sensitive fuze, the sensitivity of which is largely independent ofthe actual light intensity but which is sensitive to a given fractionalchange of th light intensity existing at the time of use. l Y

An additional object is to provide a light-sensitive fuze having awindow or lens which admits maximum light in a predetermined directionand has a narrow angle of optical field.

A further object is to provide a light-sensitive device which is equallysensitive to light striking the photoelectrie cell from any angularposition around the axis of the cell, at a predetermined inclination tothe axis.

Another object of the invention is to provide an improved electricalcircuit for use with a light-sensitive fuze.v

Still another object of the invention is to provide a fuze having asquib operable by rthe plate current of a thyratron which is triggeredby an amplied impulse from a photoelectric cell.

A still further object is to provide mechanical improvements for makinga reliable and satisfactory lightsensitive fuze.

An additional object is to provide a light-sensitive fuze which may beused with a bomb, shell, or other explosive device so that groundapproach will cause the bomb, for instance, to explode and scatterfragments downward, for greater elfectiveness against personnel.

These and other objects of the invention may be better understood byreference to the accompanying drawings, in which Figure 1 is alongitudinal sectional view of one form of the new fuze adapted for use:on a bomb;

Figures 2-7, inclusive, are sectional views on the lines 2-2 to 7-7,inclusive, respectively, in Fig. 1;

Figure 8 is a detail sectional View on the line 8 8 in Figure 6, showingthe arming and self-destruction switches;

Figure 9 is a side elevational view of a bomb, with parts broken away,showing the photoelectric proximity fuze mounted `thereon and connectedto the arming wire;V

Figure 10 is a sectional view on the line 10-10 in Figure l;

Figure l1 is a sectional view on the line 11-11 in Figure 5;

Figure 12 is a sectional view on the line 12-12 in Figure l;

Figure 13 is a detail sectional view on the line 13-*13 in Figure 7 i,showing plug and socket connections for coupling parts of the fuze, and

Figure 14 is a diagrammatic view of the wiring circuits for the fuze. v

The new fuze is illustrated in a form suitable for use on Y the tailportion of a bomb, although it will be understood that the fuze may beused on the nose of the bomb and on other types of projectiles.

Referring to the drawings, the numeral 20 indicates the fuze casingwhich is of cylindrical shape and is formed` of metal of suitablethickness to insure ruggedness. The casing 20 is open at its rear endwhere it receives a pho toelectric cell unit 21 including rear and frontsections sections 22 and 23 are secured to the lens Vby suitable bolts(not shown) ex-tending through the sections and the lens. Thus, the lensis held rrnly in a xed position relative to the sections 22 and 23.

The rear section 22 is provided with an axially disposed cup 25 which isopen at its front end. The side wall of the cup extends forwardly asubstantial distance from the section 22 and terminates in a straight,annular rim 26 which is disposed substantially medially of the ends lofthe unit 21. The front section 23 is formed with a rearwardly extendingaxial sleeve 27 terminating in an annular rim 28, the rims 26 and 28cooperating to define an annular light slit 29 within the centralportion of the lens 24. The front section 23 is also provided near itsperiphery with a forwardly extending sleeve 23h which fits closely inthe open rear end of the casing 20. The photoelectric unit 21 is heldinthe casing by a plurality. of screws 20a extending through the casingand threaded into the sleeve 23b.

t Mounted in the sleeve 27 and extending into the cup 25 is aphotoelectric tube or photo-voltaic cell 32 having v its cathode orlight sensitive element 32a disposed slightly to the rear of the slit29. A clamping ring 33 is secured to the front face of section 23, as bymeans of screws 33a, and serves to hold the tube in position against anannular inclined surface 23C on the section. The tube 32 is cushioned bymeans of annular rubber pads 34 and 35 disposed between the annulus ofthe tube and the surface 23c and the ring 33, respectively.- The'tube 32may be of any suitable construction,'such as that shown in a copendingapplication of I. E. Henderson et al., Serial Number 568,020, filedDecember 13, 1944, and now abandoned.

Connected to the front section 23 of the photoelectric cell unit 21 is aframe including opposed side rails 36, the rear ends of which aredoubled over and secured to the sleeve 23b by means of screws 37. Attheirfront ends, the rails 36 are bent inwardly and secured to the rearface of an insulating plate 38, as by means of bolts 39 and nuts 40.Mounted on the rear face of the plate l38 is a clockwork mechanism42.which may b e of con,-

ventional design. The clock mechanism 42 is normally locked againstoperation by a transverse plunger 43 (Fig. which is urged outwardlytoward a clock-releasing position by a compression spring 44. Theplunger 43 is slidably mounted in a bracket 45 secured to the insulatingplate 38, and the spring 44` is seated at its inner end on the bracket45 and at its outer end against a button 46 on the plunger. At its outerend, the button 46 engages a stop 47 slidably mounted in a hollow boss48 on the casing 20. The stop 47 is normally held against outwardmovement in the boss by means of an arming wire 49 extendingtransversely through the boss, whereby the plunger 43 is held in itsretracted position for locking the `clock 42 against operation. The stop47 is retained in the boss 48 by a pin 50 extending transversely throughthe boss and through a longitudinal slot in the stop. It will beapparent that when the arming Wire 49 is withdrawn from the boss 48, thestop 47 is released and allows the spring 44 to move plunger 43outwardly so as to release the clock.

A bail 51 is pivotally mounted on a pin 51a on the bracket 45, andbefore the fuze is assembled in the casing 20, the plunger 43 is pressedinwardly against spring 44 to its clock-locking position where it isheld temporarily by swinging the bail 51 on its pivot until thetransverse portion of the bail overlies the plunger button 46. Theplunger 43 is then released, and as the fuze parts including plate 38and rails 36 are inserted in casing 20, the rear end of the casingengages the transverse portion of bail 51 and forces it rearwardly outof line with the plunger 43. The latter is then held in its retractedposition by the inner wall of the casing 20 until the fuze assemblyincluding plate 38 and rails 36 reaches its innermost position in case20, where the plunger is held retracted by engagement with the stop 47.

The clock mechanism 42 includes a driven shaft 42a which extends throughthe plate 38 and is adapted to operate a switch assembly 53 including anarming switch 54 and a self-destruction switch 55 mounted on the frontface of plate 38. An insulating segment 56 is mounted on the front endof clock shaft 42a and is normally positioned between contact springsforming the switches 54 and 55. That is, the arming switch 54 includes apair ot switch springs 54a'and 54b (Figure 8) which are northeself-destruction switch 55 includes a pair of switch mally separatedfrom each other by the segment 56, and springs 55a and 55b which alsoare normally separated by the segment 56, whereby the switches are heldopen. When plunger 43 releases the clock mechanism 42, the latter drivesthe insulating segment S6 which, after a predetermined period of time,disengages the arming switch springs 54a and 54h, thereby causing thearming switch to close. Further rotation of segment 56 causes theself-destruction switch 55 to close after an additional time interval,due to disengagement of the segment from the switch springs 55a and551;.

An electrical plug 58 is mounted in an opening in i11- sulating plate 38where it is held on a bracket 59. The plug 58 (Figure 6) is providedwith a plurality of prongs, numbered serially from l-lO, inclusive, theprongs projecting forwardly into sockets 60 mounted on an insulatingplate 61 in the casing 20. As shown in Figure 12, the sockets 69 arenumbered serially from 1-10, inclusive, to correspond to the respectiveplugs which they receive. The plate 61 is disposed in front of plate 38in spaced relation thereto, and the sockets 60 are secured to plate 61by means of rivets 62 extending through the plate. At their front ends,the rivets 62 are connected to wiring 63, as by means of solderedjoints.

The plate 61 forms the rear end of a battery casing 64 which includes agenerally U-shaped frame 65. The ends of the leg portions of the frame65 are bent inwardly, as shown at 65a, and are connected to the plate 61by bolts 66 and nuts 66a. Thus the bight portion of the frame 65 formsthe front end of the battery casing,

and the legs of the frame 65 are disposed in closely adjacent relationto the inner wall of casing 20. A retaining plate 67 is secured to eachof the legs of the frame 65. Between the retaining plates 67 are thebattery elements which comprise an A battery 68, a B battery 69 made upof a plurality of serially connected cells, a C mattery 70 (Figure 14),and a battery condenser 71. The condenser and the cells constituting theA, B and C batteries are encased in a potting compound 72 which providessuitable insulation and protection against the elements. It also servesto protect the parts against mechanical shock.

An amplifier and thyratron unit i4 is disposed in the casing between thecell unit 21 and the clock mechanism 42, the unit 74 being electricallyconnected by wiring 75 through the plug 58, sockets 60 and wiring 63 tothe battery unit 64. The amplier and thyratron unit 74 is mounted on aninsulating plate 76 secured to the rails 36 by brackets 77 and 77a,respectively, the brackets being connected to the rails by screws 78. Aresilient pad 79 is folded around the insulating plate 76 adjacent eachof the brackets 77 and 77a, the insulating plate and pads beingconnected to the brackets by bolts 80. Thus,

the plate 76 is resiliently connected to the side rails 36 throughbrackets 77 and 77a, whereby the amplifier and thyratron unit is betteradapted to withstand mechanical shock.

The amplifier and thyratron unit 74 includes amplifier tubes 82, 83 and84 and a thyratron 85. The tubes 82 to 85, inclusive, are held inposition on the rear face of plate 76 by clips 86 of brass or othersuitable material. As shown in Fig. l0, the clips 86 are secured to therear face of plate 76 by rivets 87 which extend through the plate andalso serve to connect a retaining strap 88 to the front face of plate76. The end portions of strap 88 extend forwardly and are interconnectedby a strip 89, the ends of which are turned over the ends of strap 88,as shown at 89a. Thus, the strap 88 and the interconnecting strip 89form a retainer for the necessary resistors, condensers and othercomponents 90, all of which may be encased as a unit in a suitablepotting compound (not shown).

The tubes 82 to 85, inclusive, the resistors and condensers 90, and thebatteries 68, 69, and 70 are electrically connected with thelight-sensitive device 32 and switches 54 and 55 in a circuit which isshown diagrammatically in Fig. 14. As there shown, the cathode 32a ofthe tube 32 is connected through a resistor 92 and one of the prong andsocket connections 58a, 60 to a tap 93 on the B battery 69, while theanode of the tube 32 is connected to the control grid 82a of the iirstamplifier tube 82. One terminal of each of the tube laments 82b, 83b,8411 and 85b is connected by a wire 94 through another prong and socketconnections 58a, 60 to the positive side of A battery 68, and the otherterminal of each tube iilament is connected by a wire 95 to a terminal95a which, in turn, is connected to the plunger 43. The plunger 43,which is grounded to the battery casing 20, forms one element of `aswitch, the other element of which comprises a pair of switch arms 96mounted on the insulating plate 38. When the plunger 43 is in its normalretracted position, it is out of engagement with the spring arms 96, sothat the switch 43, 96 is open. However, when the plunger 43 is releasedby arming wire 49, it engages the spring arms 96 so as to complete thecircuit from the tube filaments to the negative side of A battery 68.

The screen grids 82C, 83C, and 84C of the amplier tubes are connectedthrough a Wire 97 to a second tap 93a on the B battery 69. Each of thetube plates 82d, 83d and 84d is connected through a load resistor 98 andshunt condenser 98a to a wire 99 which leads through another of theprong and socket connections 58a, 60 to the positive side of B battery69, an additional load resistor 10i) being interposed between the wire99 and bination to provide a heavy `iilter arrangementforltering outbattery noises and transients, and to attenuate'the low frequencysignals needed to subsequently fire the detonator unit. A wire 101 isconnected between the resistors 98 and 100 and leads throughbatterycondenser 71 to a common battery terminal102 connected to the negativeside of the B battery 69, the positivey side of C battery 70 and thenegativeside of A battery 68.

V`Grid bias resistors 90a are connected 'between the control grids ofthe amplifier tubes 82, 83 and 84 and the wire 95 to provide the properbias von the grids.'` The amplier tubes are coupled'by couplingcondensers 90b and resistors 90C, and the output' of the third amplifiertube 84 is coupled to the control grid 85a of the thyratron by anothercoupling condenser 90b. A by-pass condenser 90d is coupled between thewire 95 and each of the control grids 83a and 84a. The control grid 85aof the thyratron is connected through a grid bias resistor 103 and wire104 to the negative side of C battery 70, so that the proper bias isimposed upon the thyratron grid. A by-pass condenser 105 is coupledbetween the thyratron plate 85d and -wire 95. Y

The output of thyratron 85 is conducted through wire 106 and armingswitch 54a, 54b to one side of an electrically operable squib ordetonator 107, the other side of which is connected to wire 99 and thepositive side of B battery 69. The contact arm 55a `of theselfdestruction switch 55 is connected through a resistor 108 to a pointbetween the squib 107 and the arming switch 54, the other contact 55h ofthe self-destruction switch being connected through a wire 109 to theterminal 95a. It will be apparent that when arming switch 54 is closed,as previously described, the squib 107 is connected at one side to thepositive terminal of battery 69 and at the other side through switch 54to the plate of thyratron 85, the filament of which is connected to thenegative side of battery 69. Accordingly, when the thyratron istriggered, the detonator 107 is operated. Also, if the detonator 107 hasnot been operated prior tok closing of the self-destruction switch 55,as previously described, the latter switch upon closing will complete adetonating circuit from the positive side of battery 69 through thedetonator 107, the ten ohm resistor 108, self-destruction switch 55,terminal 95a, and switch 43--96 to the negative side of battery 69.

In the use of the new fuze, as shown, the casing 20 is mounted on thetail portion of a bomb 110, the front end of the casing tting closely inan adaptor 111 on the bomb. The adaptor 111 is slit longitudinally, andthe segments deiined by the slits are clamped together against casing 20by a releasable clamping ring 111a. The fuze casing 20 is housed withinand protected by a tail assembly 112 on the bomb, the photoelectric unit21 projecting rearwardly from the rear end of the tail assembly. In thenose portion of the bomb 110 is the usual mechanical `fuze 113 which maybe used in lieu of or in conjunction with the proximity fuze 20. Thefuze 113 is armed by a propeller 114 .which is normally locked by thearming wire 49 extending along the bomb casing and through the hollowboss 48, the intermediate portion of the arming wire 49 being connectedto a iixture 115 on the airplane or other vehicle carrying the bomb.

In operation, when the lbomb is released, the arming wire 49 iswithdrawn from the propeller 114 and from the hollow boss 48, thusreleasing the propeller 114 and -across A battery 68 and are heated sothat the fuze is prepared for operation upon closing of the armingswitch 54. Y It been found that for safety purposes the arming switch 54should "remain open for approximately six seconds after releasing thebomb, at which time the bomb will be approximately 600 feet below thebombing plane. It will be understood that safetydevices other than andin addition tothe'switches 43--96 and 54ag-'54b may be used. i and thelight-sensitive element of the tube 32, within a The operation of thefuze is dependent upon the percentage change in the quantity of lightreaching the lens` 24 narrow angle which may be called the width oftransmission zone and which maybe defined as Ytheyangular separationbetween two directions in a plane through the axis of the fuze, in eachof which the transmission of the lens-slit system is half the maximumtransmission.` The forward angle is delined as the angle betweena planenormal to the axis of the fuze and a line midway between the twodirections deiining the transmission zone. It will be apparent that theforward angle is dependent upon the relative positions of the lens 24,the annular slit 29 and the light-sensitive element or cathode 32a ofthe tube 32. With the construction described, light striking the cathode32a of the tube 32 in appreciable quantity will, due to the design ofthe lens and slit system, come from a narrow region bounded by twoconical surfaces and inclined forward. It will be understood that theforward angle may be varied to suit particular conditions.

The percent light signal may be expressed as the fraction or percentpeak signal relative to the background light level. The Sensitivity isdefined as lthe voltage output at the thyratron grid a, divided by thepeak percent light signal. The threshold is defined as the peak percentlight signal required to trigger the thyratron 85. Sensitivity andthreshold are dependent upon the form of signal, but for any given formof signal the threshold, T, and sensitivity, S, are related as follows:

where C is the thyratron bias Voltage, Vg(crit.) is the critical bias atwhich the thyratron fires, and V(crit.) is the critical signal requiredto re the thyratron.

When the bomb approaches a target, such as an airplane, a certain amountof sky light which would otherwise reach the photoelectric tube 32through the lens 24 is obscured by the airplane, and a sudden reductionof electron output from the light-sensitive cathode of the tube 32occurs, since the bomb is traveling at high speed. This sudden decreaseof electron emission from the cathode of the tube 32 results in acurrent pulse or a change in the bias on grid 82a of the first amplifiertube 82. This current pulse is amplified by the tubes 82, 83 and 84, andthe ampliiied pulse acts on the control grid 85a of the thyratron tocause the latter suddenly to become conducting and tire the detonator107. Preferably, the electrical componentsv are so designed that thethyratron 85 will be triggered when the light reaching the photoelectric tube 32 is reduced by even as little as one percent, due tointerception of some of the light by the target.

For test purposes, we provide a conductor 117 connected between thecontrol grid 85a of the thyratron and the adjacent couplingcondenser'90b and leading to a contact 118 mounted in a receptacle 118a(Figure 5) accessible from outside the casing 20. An additional testwire 119 is connected between Contact 55a of the self-destruction switchand resistor 108 and leads to a contact 120 mounted in a plug 120a(Figure 5) accessible from outside the casing through a removable cap121. It is the function of the ten (l0) ohm resistor 108 to assist ingiving a ring indication of the detonator 107 at contact 120 for testpurposes.

The new li-ght-sensitive fuze, in combination with an explosiveprojectile, provides an eifective weapon for attacking and destroyingenemy aircraft. In addition, the fuze may be used in causing bombs toexplode on ground In a photoelectric fuzel, Ha` casing, a ,photo-relectric cell u`nit mounted atonel end of the casing, a framefmounted inthe casing `adjacentfthe cell unit and removable from thecasing,janfamp1iergand',thyratro electrically coupled to said cell andmountedon the frame,`

`a detonator,y means for coupling'the Ithyratron tothe detonator forfiring the detonator upon triggering of the vthyratron by an amplifiedcurrent` pulse from the cell unit,

a safety device 01'1 `the frame' for rendering said coupling means andsaid amplifier andthyratron inoperative, said mnpliler,y thyratron andsafety devcebeing removable t fromfthe casing ori the fraxile` as aunit,`a battery assembly in the casingadjacent lthe frame, and releasablemeans for 3electricallyl connecting the battery to said amplifier andfthyratron.y

Referucesl ACited in the le ofthis *patent` V* UNITED STATES PATENTSSchweitzer Aug. 21, 1934 yHammam New. 10, 193,6 Wallace Nov. 2, 1937rVos 1-- 1 Nov. 22,y 1938 Logan July?, 1940 Ferrel .-..f Sept. 9, 1941

